This invention relates generally to devices capable of detecting angular deviations of a beam, and, more particularly, to a method and apparatus which is capable of detecting small angular deviations of a beam in order to provide a more precise alignment of the beam.
In today's every increasing utilization of the laser, precise alignment of the laser beam relative to other optical elements and fixed reference members becomes essential. In addition, it is often necessary to continuously monitor and dynamically align such beam. For example, in laser beam pointing systems, it is also required to dynamically maintain the alignment of the collimated laser beam.
It is recognized that diffraction gratings can produce a rapid variation in the intensity of various difracted orders of an incident beam in a narrow wavelength range and in a narrow range in the angle of incidence. This effect, the so called Wood's anomaly, is fully described within the following publications; Hessel, A. and Oliner, A., "A New Theory of Wood's Anomalies on Optical Gratings," Applied Optics, Vol. 4, No. 10, October 1965, pps 1275-1297; Palmer, C. Harvey, Jr., "Parallel Defraction Grating Anomalies," Journal of the Optical Society of America, Vol. 42, No. 4, April 1952, pps 269-276; and Palmer, C. Harvey, Jr., "Defraction Grating Anomalies, II. Course Gratings," Journal of the Optical Society of America,. Vol. 46, No. 1, January 1956, pps 50-53.
By detecting these changes in intensity (efficiency) of the diffracted beam one can ascertain if any angular deviation of the incident beam has taken place. Unfortunately, this change in intensity which occurs as a result of Wood's anomaly produces a curve of the relationship between diffraction efficiency (intensity) and angular incidence in which there is a gradual increase in efficiency to a maximum after which a rapid decrease in efficiency occurs. Consequently, small angular deviations of the incoming beam are extremely difficult to detect.
Therefore, a need arises for providing an apparatus for easily ascertaining even small angular deviations of a beam.